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alternator wont charge, code 41 on key on&off self test
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eddyb
Novice
Feb 26, 2011, 1:09 AM
Post #1 of 11
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alternator wont charge, code 41 on key on&off self test
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I've got a 92 dodge caravan with a 3.0 in it. Last week the check engine light came on, ran a self test and got a code 41. next time I drove it the light stayed out, then it returned and stayed on running the battery dead. I know that the code 41 means a short or break in the alt. field wiring. First thing I did was remove the alt. and had it bench tested, it worked fine. The next step was to check the field wire, I hooked my ohm meter to it at the alt. and the other end to pin 20 on the ecm connector and got 0 resistance, then checked other wire next to it that my book says should run to the ignition switch and got 11.7 volt reading with low battery. I then assumed that the problem must be in the ecm. as I understand that it serves as the regulator. Went and bought a high dollar rebuilt ecm.,as I couldn't locate a used one, charged the battery, and installed it only to find I have the same problem! Either I'm missing something or I've got a rebuild with exactly the same problem(unlikely)! Any one have any ideas? I'm new to this site but it looks like it will be a killer resource! Thanks, EddyB
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 26, 2011, 6:21 AM
Post #2 of 11
(1697 views)
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Re: alternator wont charge, code 41 on key on&off self test
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Did you test your charging system voltage to determine if you have a problem or not?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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eddyb
Novice
Feb 26, 2011, 7:24 AM
Post #3 of 11
(1692 views)
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Re: alternator wont charge, code 41 on key on&off self test
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Yes I did, shows 0 volts, if I charge the battery with the charger it will run fine till the injectors pump and other items drain it. I need to figure out if the ecm supplies voltage or ground to the field terminal when it's working properly so I can test further. Since my problem was intermittent when it first started I thought I'd take the alternator back in for another bench test as it might have just been working temporarily. Will let you know! Thanks, EddyB.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 26, 2011, 7:39 AM
Post #4 of 11
(1689 views)
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Re: alternator wont charge, code 41 on key on&off self test
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No, it doesn't read "0" volts. Read the voltage across the battery with the engine idling and no accessories on.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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eddyb
Novice
Feb 26, 2011, 7:51 AM
Post #5 of 11
(1685 views)
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Re: alternator wont charge, code 41 on key on&off self test
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You're right, just waking up here! My 0 voltage comes from the alt field wire that runs to the ecm. I'll go check it out and let you know what it reads.
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autojoe
User
Feb 26, 2011, 8:06 AM
Post #6 of 11
(1684 views)
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Re: alternator wont charge, code 41 on key on&off self test
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best way to troubleshoot a code 41 is with a scan tool.second best is with a frequency counter,tachometer,or dwell meter to the field control wire of the alternator.its the dark green wire.there are 2 small wires on back of alternator.one is field power and other is field control.with engine running connect a voltmeter to each of these wires.first one then the other.one should read almost exact battery voltage that is found across the battery terminals.the other should be slightly lower.if they are both the same there is probably an open between the alternator and the computer.next choose a meter that can detect and confirm a pulsing dc voltage.connect this meter to the field control wire,the one with the lower voltage.if both terminals had the same voltage,try to detect a pulse on both wires.on the frequency counter,one of the wires should read a frequency greater than zero.on a tachometer,one of the wires should read an rpm greater than zero.on the dwell meter set on the four cylinder scale one of the wires should read a dwell greater than 0 degrees but less than 90 degrees.if the readings are outside the range of the specifications given above,check the dark green wire to the computer for continuity.if the wire is good replace the computer.I use a labscope or a meter with frequency on it.
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eddyb
Novice
Feb 26, 2011, 9:40 AM
Post #7 of 11
(1671 views)
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Re: alternator wont charge, code 41 on key on&off self test
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Checked battery voltage, 11.8 after it started. Going to pull alt. and have it retested, if it checks out, not sure where to look next. Saw that tip on checking battery drain in another post, need to commit that one to memory bank!
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eddyb
Novice
Feb 26, 2011, 11:08 AM
Post #8 of 11
(1668 views)
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Re: alternator wont charge, code 41 on key on&off self test
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Tried your idea, like you said. Had full battery voltage to supply terminal, control terminal had fluctuating voltage in millivolt range, hooked up my old tach dwell meter and got 0 readings on both tach. and dwell. Have already checked the green wire from terminal on alt. to pin #20(the other end) at ecm. with ohm meter. Shows 0 resistance. Would it hurt any thing toskin back the wire just behind the pin and run a jumper to the alt. just in case I'm moving something around when I disconnect it to test? Starting to look like I bought an ecm. with the same problem I've already got. Thanks EddyB
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autojoe
User
Feb 26, 2011, 2:23 PM
Post #9 of 11
(1646 views)
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Re: alternator wont charge, code 41 on key on&off self test
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was it a used junk yard computer?
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eddyb
Novice
Feb 26, 2011, 5:37 PM
Post #10 of 11
(1643 views)
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Re: alternator wont charge, code 41 on key on&off self test
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NO it was rebuilt, Your response helped me out though. After you told me one wire was supply voltage and the other was control I figured that the control circuit had to be grounding through the computer. I grounded the wire at the alternator and charge voltage kicked up to 15.5. I knew I was on the right track! Scratched my head for quite awhile and then started looking for crappy ground connections. Found an 8 or 6 gauge connection on the left fender well that was pretty rusty, cleaned it up and everything is working fine. Going to go back out and try my old ecm. as I hadn't turned in the core yet, if it works(this is the best part) my supplier is willing to let me return the new one!!! I guess the ecm. must rely on more than 1 ground connection as the car was running alright otherwise. Thanks for your insight!!! I plan to watch this web sight, although I'm a shade tree, I might be able to help someone else sometime! Thanks again, EddyB
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autojoe
User
Feb 26, 2011, 6:03 PM
Post #11 of 11
(1639 views)
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Re: alternator wont charge, code 41 on key on&off self test
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that is good to hear.lots of knowledgeable people on this site.
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